1. Field of the Invention
The present invention relates to an organic light emitting display and a method of fabricating the same, and more particularly, to an organic light emitting display in which differential pressure is controlled to prevent Newton's rings from being generated and a method of fabricating the same.
2. Description of the Related Technology
Recently, organic light emitting displays are widely used for its relatively simple structure. The organic light emitting display is a self-emission display in which an organic layer is used as an emission layer. Since the organic light emitting display does not need a back-light for emitting light unlike a liquid crystal display (LCD), the thickness and weight of the organic light emitting display are small. Therefore, the organic light emitting display has been actively developed as a display panel of a portable electronic device such as a portable computer, a mobile telephone, a portable game apparatus, and electronic books.
In an organic light emitting display, one or more organic layers including an emission layer are interposed between first electrodes and second electrodes. The first electrodes are formed on a substrate and function as anodes for injecting holes. The organic layers are formed on the first electrodes. Second electrodes that function as cathodes for injecting electrons are formed on the organic layers to face the first electrodes.
When moisture and oxygen are permeated from the outside to organic light emitting diodes (OLED) in the organic light emitting display, the electrodes are oxidized and separated from each other. In such a case, the life of the OLEDs is reduced, and emission efficiency deteriorates. In addition, emission colors may change.
Therefore, in the fabrication of the organic light emitting display, a sealing process for protecting the OLEDs from the outside may be performed. In one method, a polymer such as polyethyleneteraphthlate (PET) may be laminated on the cathodes of the OLEDs. In another method, a cover or a cap formed of a metal or glass includes an absorbent. In addition, a nitrogen gas may be filled in the cover or the cap. The edges of the cover or the cap may be capsule sealed by a sealant such as an epoxy resin.
However, since it is not possible to completely prevent moisture and oxygen from being permeated from the outside to the OLEDs by the above-described methods, the OLEDs may deteriorate and change.
In order to solve the above problem, a capsule sealing up method in which a frit as a sealing material is used to improve a moisture-proof property between an element substrate and a cap has been proposed. According to U.S. Patent Publication No. 20040207314 in which a structure of coating a glass substrate with a frit to seal up an OLED is disclosed, since a gap between a first substrate and a second substrate is completely sealed up using the frit so that it is possible to effectively protect the OLED.
In the structure where the OLED is sealed up using a sealing substrate coated with the frit, the distance between the substrate and the sealing substrate is smaller than the distance between the substrate and the sealing substrate in a structure where the absorbent is used. Also, in manufacturing the organic light emitting display sealed with the frit, a plurality of display panels are simultaneously fabricated on a mother substrate. Then, the mother substrate may be cut into individual unit display panels. The center of the substrate may be curved down due to the weight of the substrate.
In such an OLED, light incident on the substrate from the outside generates optical interference to form concentric rings at connection points of the sealing substrate. These concentric rings are referred to as Newton's rings. The phenomenon of Newton's rings is an interference pattern caused by the reflection of light between two surfaces: a spherical surface and an adjacent flat surface. It appears as a series of concentric, alternating light and dark rings centered at the point of contact between the two surfaces. The Newton's rings deteriorate the quality of an image during the operation of OLEDs. The discussion in this section is to provide general background of the invention and does not constitute an admission of prior art.
The discussion in this section is to provide background of the related technology, and does not constitute an admission of prior art.